Technical Field
The present disclosure relates to a position indicator, and particularly to a position indicator used as an input pen for a capacitive touch panel.
Description of the Related Art
Tablet terminals that have been popular in recent years generally use a capacitive touch panel as a touch panel for receiving touch input. The capacitive touch panel typically has a configuration in which a plurality of X-electrodes each extending in a Y-direction and a plurality of Y-electrodes each extending in an X-direction are arranged so as to intersect. The capacitive touch panel is for example configured to repeat, for all of the Y-electrodes in order, processing of a determined input signal to a Y-electrode and extracting this signal from each X-electrode in order. When a finger approaches the touch panel, a capacitance occurs between the finger and an X-electrode and a Y-electrode in the vicinity of the finger, and a human body absorbs a current through this capacitance. The amplitude of a signal extracted from the X-electrode is therefore decreased. The capacitive touch panel is configured to detect the position of the finger by detecting the change in the amplitude.
The capacitive touch panel is basically intended for finger detection. However, a large number of electronic pens compatible with capacitive touch panels have been sold in recent years. U.S. Pat. No. 8,766,954 and Japanese Patent No. 4683505 (hereinafter referred to as Patent Documents 1 and 2) disclose examples of electronic pens of this kind. As is shown also in Patent Documents 1 and 2, in a case where an electronic pen is used on a capacitive touch panel, a low capacitance occurring between the electronic pen and electrodes within the touch panel may become a problem. Formerly, in order to solve this problem, a pen point of the electronic pen has been made thick to increase an area of contact with the touch panel. However, the thick pen point is not suitable for drawing a thin line. There has accordingly been a desire to develop an electronic pen that can ensure a high capacitance between the electronic pen and electrodes within the touch panel while having a thin pen point. Patent Documents 1 and 2 disclose examples of such electronic pens.
FIG. 6 is a diagram depicting an example of an electronic pen (position indicator) that may facilitate providing a high capacitance between the electronic pen and electrodes within a touch panel while having a thin pen point. As depicted in FIG. 6, an electronic pen 101 according to the present example includes, as a configuration viewed from the outside, a cylindrical casing 102, a pen point portion 103 disposed at a tip of the casing 102, and a base portion 104 having the shape of a circular cone which base portion is disposed between the pen point portion 103 and the casing 102, and is configured to surround the periphery of the pen point portion 103. The pen point portion 103 is formed by a conductor. The pen point portion 103 is formed so as to be sufficiently thin. Hence, this electronic pen 101 is also suitable for drawing a thin line.
A circuit 105 is formed within the electronic pen 101. As depicted in FIG. 6, the circuit 105 includes resistance elements 150 and 151, inverter circuits 152 and 153, a power supply 160, and power supply wirings GH and GL. The resistance element 150 has one end coupled to the pen point portion 103, and has another end coupled to an input terminal of the inverter circuit 152. The resistance element 151 is disposed in parallel with the inverter circuit 152. An output terminal of the inverter circuit 152 is coupled to an input terminal of the inverter circuit 153. An output terminal of the inverter circuit 153 is coupled to the casing 102. The casing 102 is grounded through a human body of a human holding the electronic pen 101.
The power supply wiring GH is commonly coupled to a high-level side terminal of the power supply 160 and respective high-level side power supply terminals of the inverter circuits 152 and 153. In addition, the power supply wiring GL is commonly coupled to a low-level side terminal of the power supply 160 and respective low-level side power supply terminals of the inverter circuits 152 and 153.
When the pen point portion 103 approaches a touch panel, not depicted in FIG. 6, a signal S1 is supplied from the touch panel to the pen point portion 103, as depicted in FIG. 6. This signal S1 is inverted by the inverter circuit 152, and thereafter supplied to the inverter circuit 153. The inverter circuit 153 tries to further invert and output the thus supplied inverted signal of the signal S1. However, the inverter circuit 153 cannot perform the output because the output terminal is grounded, and as a reaction, the reference potential and ground potential of the circuit 105 swing. This swing causes a signal S2 having a polarity equal to that of the inverted signal of the signal S1 to be generated at various positions of the circuit 105, as depicted in FIG. 6. When the thus generated signal S2 is radiated to the outside through the pen point portion 103 and reaches the touch panel, a larger amount of signal appears to have been absorbed by the electronic pen 101 as viewed from the touch panel. This is equivalent to an increase in capacitance between the electronic pen and electrodes within the touch panel. Thus, according to the configuration depicted in FIG. 6, it is possible to provide the electronic pen 101 that has a high capacitance between the electronic pen 101 and electrodes within the touch panel though the pen point portion 103 is formed so as to be thin, and which electronic pen can therefore be suitably used as an input pen for a capacitive touch panel.
However, the configuration of such an electronic pen 101 has a problem of consuming a large amount of power and a problem of a possibility of radiating an unnecessary signal to the outside through the casing 102. That is, the generation of the signal S2 at various positions of the circuit 105 is equal to driving all of the stray parasitic capacitances in small amounts at the various positions of the circuit 105. Hence, the inverter circuit 153 needs to be supplied with a high power in order to radiate the signal S2 of a sufficient strength from the pen point portion 103 to the outside. As a result, the power consumption of the electronic pen 101 is increased. In addition, when the electronic pen 101 is not held by a human, the casing 102 is in an electrically floating state. When the output signal of the inverter circuit 153 is supplied to the casing 102 in the electrically floating state, the output signal is radiated to the outside through the casing 102.